It is known, as reported in a book by Kosikowski, "Cheese and Fermented Milk Foods", 1966, to manufacture skim milk cheese by a cheddar cheese process. In this diet and calorie-conscious era, skim milk cheddar cheese would appear to be highly desirable. However, as reported in the Kosikowski reference, skim milk cheese made by a cheddar cheese process is without much cheese flavor and the body texture of skim milk cheddar cheese is very hard. Rapid drying out of the skim milk cheese during cooking in the vat is a characteristic feature, despite the use of low cooking temperatures of 88.degree. F.
In one method for the manufacture of cheddar cheese, a batch of milk is placed in a cheese vat and is inoculated with a lactic acid starter. After the desired degree of lactic acid development has been attained, rennet is added to set or coagulate the milk. When the resulting curd has attained the proper degree of firmness, the curd is cut into cubes with curd knives. The curd is then agitated in the whey and heated to a temperature of about 100.degree. F. to about 105.degree. F., the heating of the curd to the desired temperature, preferably takes place over a period of about 30 minutes. The curd is held at this temperature and agitation of the curd is continued until the acidity of the whey reaches about 0.13 to 0.16, expressed as percent lactic acid or its equivalent, at which time the heating is terminated and the whey is drained from the cheese vat. Usually, the temperature is maintained for about one hour. The mass of curd is then formed or "ditched" to facilitate whey drainage.
The curd is then allowed to knit and drain after which it is cut into blocks or slabs which are turned on the bottom of the vat. After about one hour, the slabs are stacked, cut and restacked by hand during which time the acidity of the curd increases and further amounts of whey are expelled from the curd. The cutting, turning and stacking of the cheese curd in the cheese vat is known as "cheddaring". Cheddaring is usually continued for a period of about two hours until the desired knit and smoothness of curd is achieved. The cheese curd is then milled into small pieces which may be washed, after which the curd is salted with an amount of salt to provide a total salt content of from about 1.65 to 1.9 percent by weight of the curd. The salted curd is then placed in hoops and pressed overnight. The pressed curd is then wrapped and cured until the desired flavor characteristics are attained.
Cheddar cheese has a fat content of at least about 50% on a dry basis and has not more than 39% moisture. After the moisture of the curd has been reduced to less than about 39%, the cheddar curd containing 50% fat, dry basis, does not undergo any further syneresis or expulsion of whey.
Washed curd (or soaked curd) cheese is a semisoft to slightly firm cheese that is made in the same way as cheddar except that the milled curd is washed with water before it is salted. "Soaked curd" usually indicates a longer washing period that "washed curd".
The curd is matted and milled as in making cheddar. Then water is added, and the curd is stirred in the water for several minutes, or as long as half an hour, as it cools. Part of the whey is extracted, and water is absorbed by the curd during this process. Then the curd is drained, salted and pressed as in the cheddar process.
Washing the curd increases the moisture content of the cheese, reduces the lactose content and final acidity, decreases body firmness and increases openness of texture. Washed curd cheese does not keep as well as cheddar. Usually it is cured for only 1 or 2 months. If it is made from raw milk it must be cured for at least 60 days unless it is to be used in manufacturing.
The final analysis of washed curd cheese is: moisture 40% (not more than 42%), fat in the solids, not less than 50%, and salt, 1.4% to 1.8%.
Many improvements have been directed in the cheddar cheese manufacturing operation to reduce the time required for draining the whey from the curd to attain the proper level of moisture. U.S. Pat. Nos. 3,969,995, 4,049,838 and 4,234,615, all to Krueger, et al. are directed to the use of a drainer blade which is inserted into a mass of cheddar curd. The drainer blade is V-shaped and has a number of holes for drainage of whey. As reported in the Krueger, et al. patents, the drainage time can be reduced to as little as 15 minutes after the drainer blades are inserted into the mass of curd and pressure is applied. The '615 Krueger patent reports uniform moisture attained in the curd block after pressing times of about 15 minutes to attain moisture contents in the range of about 37% to 42%. No further draining is required after the pressing step utilizing the drainer blades since no further syneresis of whey occurs in the cheddar curd.
In the manufacture of skim milk cheddar cheese, however, syneresis of whey takes place for a substantial period after the curd has been pressed utilizing drainer blades or other means to remove moisture. The syneresis takes place as the pH of the skim milk cheddar curd continues to drop as shown in FIG. 3. If the skim milk cheddar curd is placed into fiber drums lined with a plastic bag, the whey which is expelled from the curd collects inside the bag and sometimes causes the bag to break. Since the fiber drums are not water tight, the whey exits from the fiber drums onto the storage room floor. When steel drums are used to replace the fiber drums, a skim milk cheddar curd is produced which has substantial variations in moisture from the center to the edge and from the top to the bottom. Also, the syneresed whey is held in contact with the curd, which causes excessive proteolysis of .alpha.-casein. Skim milk cheese with too little proteolysis will result in uncooked curd when the skim milk cheese is processed into a low fat or no fat processed cheese product. Excessive proteolysis results in a soft and bitter processed cheese product.
Accordingly, it is a principal object of the present invention to produce a skim milk cheddar cheese which has a uniform level of moisture throughout a large curd block. It is another object of the present invention to provide a skim milk cheddar cheese which has desirable organoleptic properties.